using System;
using System.IO;

namespace MimeCloud.Media.Video.Flv
{
    /// <summary>
    /// Reads the meta information embedded in an FLV file
    /// </summary>
    public class FlvMetaDataReader
    {
        /// <summary>
        /// Reads the meta information (if present) in an FLV
        /// </summary>
        /// <param name="path">The path to the FLV file</returns>
        public static FlvMetaInfo GetFlvMetaInfo(string path)
        {
            if (!File.Exists(path))
            {
                throw new Exception(String.Format("File '{0}' doesn't exist for FlvMetaDataReader.GetFlvMetaInfo(path)", path));
            }
            bool hasMetaData = false;
            double duration = 0;
            double width = 0;
            double height = 0;
            double videoDataRate = 0;
            double audioDataRate = 0;
            Double frameRate = 0;
            DateTime creationDate = DateTime.MinValue;
            // open file 
            FileStream fileStream = new FileStream(path, FileMode.Open);
            try
            {
                // read where "onMetaData"
                byte[] bytes = new byte[10];
                fileStream.Seek(27, SeekOrigin.Begin);
                int result = fileStream.Read(bytes, 0, 10);
                // if "onMetaData" exists then proceed to read the attributes
                string onMetaData = ByteArrayToString(bytes);
                if (onMetaData == "onMetaData")
                {
                    hasMetaData = true;
                    // 16 bytes past "onMetaData" is the data for "duration" 
                    duration = GetNextDouble(fileStream, 16, 8);
                    // 8 bytes past "duration" is the data for "width"
                    width = GetNextDouble(fileStream, 8, 8);
                    // 9 bytes past "width" is the data for "height"
                    height = GetNextDouble(fileStream, 9, 8);
                    // 16 bytes past "height" is the data for "videoDataRate"
                    videoDataRate = GetNextDouble(fileStream, 16, 8);
                    // 16 bytes past "videoDataRate" is the data for "audioDataRate"
                    audioDataRate = GetNextDouble(fileStream, 16, 8);
                    // 12 bytes past "audioDataRate" is the data for "frameRate"
                    frameRate = GetNextDouble(fileStream, 12, 8);
                    // read in bytes for creationDate manually
                    fileStream.Seek(17, SeekOrigin.Current);
                    byte[] seekBytes = new byte[24];
                    result = fileStream.Read(seekBytes, 0, 24);
                    string dateString = ByteArrayToString(seekBytes);
                    // create .NET readable date string
                    // cut off Day of Week
                    dateString = dateString.Substring(4);
                    // grab 1) month and day, 2) year, 3) time
                    dateString = dateString.Substring(0, 6) + " " + dateString.Substring(16, 4) + " " + dateString.Substring(7, 8);
                    // .NET 2.0 has DateTime.TryParse
                    try
                    {
                        creationDate = Convert.ToDateTime(dateString);
                    }
                    catch { }
                }
            }
            catch (Exception e)
            {
                // no error handling
            }
            finally
            {
                fileStream.Close();
            }
            return new FlvMetaInfo(hasMetaData, duration, width, height, videoDataRate, audioDataRate, frameRate, creationDate);
        }
        private static Double GetNextDouble(FileStream fileStream, int offset, int length)
        {
            // move the desired number of places in the array
            fileStream.Seek(offset, SeekOrigin.Current);
            // create byte array
            byte[] bytes = new byte[length];
            // read bytes
            int result = fileStream.Read(bytes, 0, length);
            // convert to double (all flass values are written in reverse order)
            return ByteArrayToDouble(bytes, true);
        }
        private static string ByteArrayToString(byte[] bytes)
        {
            string byteString = string.Empty;
            foreach (byte b in bytes)
            {
                byteString += Convert.ToChar(b).ToString();
            }
            return byteString;
        }
        private static Double ByteArrayToDouble(byte[] bytes, bool readInReverse)
        {
            if (bytes.Length != 8)
                throw new Exception("bytes must be exactly 8 in Length");
            if (readInReverse)
                Array.Reverse(bytes);
            return BitConverter.ToDouble(bytes, 0);
        }
    }
 
 

}
